1. Field
The following description relates to a butler matrix and a multi-port amplifier having the same, capable of splitting a single input signal into N-signals or combining N-signals into a single output.
2. Description of the Related Art
A multi-port amplifier uses a butler matrix as a passive device for splitting a single input signal into a plurality of signals (N) or combining a plurality of signals (N) into a single output. The butler matrix may use a micro-strip line, a strip line, a coaxial line or a waveguide selected according to the magnitude of a transmission signal. For a multi-port amplifier designed for a high power operation, a butler matrix is formed using a waveguide.
The butler matrix is implemented using a 3 dB hybrid having four ports for splitting and combining the power of signals. A 2×2 matrix uses one dB hybrid, a 4×4 matrix uses four hybrids and a 8×8 matrix uses twelve hybrids. The more input/output ports require the more hybrids and increase in complexity of the paths used to connect the hybrids to each other, resulting in a short circuit portion where the transmission lines cross each other. Accordingly, the butler matrix needs to have a design capable of preventing a short circuit caused by the crossing of transmission lines.
When the butler matrix is implemented using a planar type line including a microstrip line or a strip line that are stacked on top of each other, a via hole is used for isolating transmission lines. When the butler matrix is formed using a coaxial line or a waveguide having a limitation to implementing in a planar type, a bended transmission line is used to isolate transmission lines.
When the butler matrix uses a via hole that is formed through planer type lines stacked on top of each other, electrical parasitic components are created and this causes a distortion of signals and has a difficulty in using a high power. When the butler matrix uses a bended coaxial line or waveguide, a path loss is caused by the complicating structure of paths. If a crossover is formed at a crossing of lines by connecting two 3 dB hybrids to each other, the butler matrix is implemented as a planar type but this causes a phase difference as compared with a butler matrix using no crossover.
FIG. 1 is a block diagram showing a conventional 8×8 butler matrix. As shown in FIG. 1, the 8×8 butler matrix uses twelve 3 dB hybrids including a first hybrid to a twelfth hybrid H1, H2, H3, H4, H5, H6, H7, H8, H9, H10, H11 and H12 and includes transmission lines L15, L16, L25, L26, L37, L38, L47, L48, L59, L79, L510, L611, L612, L710, L811 and L812 to achieve interconnection among the first to twelfth hybrids H1 to H12. The signal flow of the 8×8 butler matrix is as follows.
An input signal is fed to one of input ports of the first hybrid H1. The fed input signal is split into two outputs having a half reduced magnitude and a 90 degree phase shift, and output through two output ports of the first hybrid H1.
The signals output from the first hybrid H1 are fed to the fifth hybrid H5 and the sixth hybrid H6, respectively. Each signal fed to the fifth hybrid H5 and the sixth hybrid H6 is split into two outputs as above described scheme, and output through two output ports of each of the fifth hybrid H5 and the sixth hybrid H6. The signals output from the fifth hybrid H5 and the sixth hybrid H6 are fed to the ninth hybrid H9, the tenth hybrid H10, the eleventh hybrid H11 and the twelfth hybrid H12. Each signal fed to the ninth hybrid H9, the tenth hybrid H10, the eleventh hybrid H11 and the twelfth hybrid H12 is split to two outputs for each of the ninth hybrid H9 to the twelfth hybrid H12 such that eight outputs are output through eight output ports of the ninth hybrid H9 to the twelfth hybrid H12. In this manner, when it is assumed that a path loss and a phase difference are not present, an input is divided into outputs each having a power level which is reduced by −9 dB as compared with the input power level.
However, among each transmission line connecting the first hybrid to the twelfth hybrid H1 to H12, there are crossings between the transmission lines L16 and L25, between the transmission lines L38 and L47, between the transmission lines L510 and L79, between the transmission lines L611 and L79 or L710, and between the transmission lines L612 and L79 or L710 or L811.
In order to prevent a short circuit due to the crossings among the transmission lines, the butler matrix may be implemented in a three dimensional structure by connecting waveguide lines in a bended structure, or may be implemented in a two dimensional structure by use of a crossover coupler at a crossing portion.
There is a need that an output of a butler matrix has the same amplitude and a constant phase difference relative to an input signal. In this regard, the transmission lines connecting the hybrids need to be designed to have the same transmission length, or the amplitude and phase needs to be adjusted according to the resultant change. In addition, a bended waveguide may increase in complexity of the paths.
In addition, if a crossover coupler is used at a crossing portion, a change in amplitude and phase is made at the crossing portion, so the changed amplitude needs to be adjusted by use of an amplitude attenuator or an active device having a gain, or the changed phase needs to be adjusted by use of a phase shifter.